Insofar as oxygenators are concerned, three main types can be distinguished. The oldest of these is probably the type where a film of blood is formed in direct contact with an oxygen-containing atmosphere. In a second type the oxygen instead is made to diffuse through a semipermeable membrane from an oxygen-containing atmosphere on the one side of the membrane to the blood on the other side. The third type, to which the device in accordance with the present invention belongs, is known as a bubble oxygenator. In this type of device, gas bubbles containing oxygen are sprayed directly into the blood so as to act directly upon the same. After the desired action, the excess gas is removed. Examples of constructions of the lastmentioned type, that is to say, of bubble oxygenators, are shown inter alia, in the following U.S. Pat. Nos: 3,175,555; 2,934,067; 3,545,937; 4,037,622; 3,468,831; 3,488,158; 3,615,238; 4,058,369; 3,578,411; 3,291,568; 4,033,724; 3,827,860; 3,853,479; 4,067,696; 4,065,264; 4,138,464; 4,138,288.